Keratan sulphate: a functional substitute for chondroitin sulphate in O2 deficient tissues?

Keratan sulphate and chondroitin sulphate can each fill space and exert swelling pressure in collagenous fibrillar matrices, but whereas the former is synthesised from glucose precursor without consuming NAD, the latter converts 2 mols of NAD for each uronate residue in the polymer chain. We suggest that the observed distribution of keratan sulphate and chondroitin sulphate in cartilage, cornea and intervertebral disc are determined by the ambient oxygen tension, and that keratan sulphate is preferentially synthesised in conditions of oxygen lack. The implications of this hypothesis in the physiology of contact lenses, cartilage degeneration, corneal scar repair and ageing are discussed.